lipids Flashcards
(27 cards)
Name the two types of lipids and state their components.
Triglycerides: One glycerol + three fatty acids.
Phospholipids: One glycerol + two fatty acids + one phosphate group.
Describe the structure of a triglyceride.
Triglycerides have One glycerol molecule.
Three fatty acids with long hydrocarbon tails (that are hydrophobic).
Joined by ester bonds via condensation reactions (releases 3 H₂O).
Explain how a triglyceride is formed.
Each fatty acid attaches via a condensation reaction forming an ester bond.
This occurs three times to form a triglyceride.
Describe the structure of a fatty acid.
A fatty acid consists of a carboxyl group (–COOH) attached to a hydrocarbon tail (R group).
All fatty acids share this basic structure, but differ in the R group (hydrocarbon tail) as the length and saturation of the hydrocarbon tail vary.
- Distinguish between saturated and unsaturated fatty acids.
Saturated fatty acids: No double bonds between carbon atoms.
Unsaturated fatty acids: At least one double bond causing a kink (bent) in the tail.
How does the structure of a phospholipid differ from that of a triglyceride?
One fatty acid is replaced with a phosphate group.
Describe the properties of the phosphate group and fatty acid tails in a phospholipid.
A Phosphate group: is Hydrophilic (attracts water).
Fatty acid tails: are Hydrophobic (repel water).
Explain how the structure of triglycerides relates to their function in energy storage.
Long hydrocarbon tails:
Contain lots of high chemical energy bonds which releases more energy when broken down and Provides twice as much energy per gram as carbohydrates.
Triglycerides are Insoluble in water:
Do not affect water potential, preventing osmosis or water entry into cells.
Form insoluble droplets: as
Hydrophobic tails face inward and glycerol heads shield from water
. Explain how the structure of phospholipids is related to their role in membranes.
Phospholipids Form bilayer in cell membranes: as
Hydrophilic heads face water (outside). And
Hydrophobic tails face inward.
Bilayer centre is hydrophobic and
Acts as a barrier to water-soluble substances.
Describe the biochemical test for lipids (emulsion test).
Shake the test substance with ethanol for 1 minute.
Pour into water.
Positive result: Milky white emulsion.
How can you interpret the intensity of the result from an emulsion test?
More lipid = more noticeable milky colour.
How does the oxygen content of lipids compare to carbohydrates?
Lipids have a much lower proportion of oxygen compared to carbohydrates.
Name five main functions of lipids in organisms.
Provides Energy supply – oxidised to release energy.
Provides Structural support– phospholipids form cell membranes.
Contributes to Waterproofing – insoluble lipids create water-resistant barriers.
Provides Insulation – thermal (heat retention) and electrical (nerve insulation).
Provide Protection – fat cushions delicate organs.
Describe the two parts of a fatty acid.
A carboxyl group (-COOH)
A hydrocarbon chain (R group)
Describe the features of saturated fatty acids.
No C=C double bonds.
Saturated with hydrogen.
Higher melting point.
And are Solid at room temperature (fats).
Describe the features of unsaturated fatty acids.
At least one C=C double bond which causes a kink.
Lower melting point.
Liquid at room temperature (oils).
What is the difference between monounsaturated and polyunsaturated fatty acids?
In Monounsaturated fatty acids there is One C=C double bond.
In Polyunsaturated fatty acids there are Two or more C=C double bonds.
Why do triglycerides store energy efficiently?
Triglyceride store energy officially due to :
Triglycerides have : Long hydrocarbon tails resulting to many C-H bonds which releases lots of energy.
Triglycerides have Low mass-to-energy ratio therefore energy stored in small volume.
Triglycerides are Insoluble (non-polar) therefore does not affect water potential preventing osmosis.
Triglycerides have High H:O ratio which release water when oxidised.
How are triglycerides broken down?
Broken by hydrolysis: water molecules added to break ester bonds separating glycerol + fatty acids.
Describe the structure of a phospholipid.
A phospholipid consists of a Hydrophilic head: glycerol and a phosphate group (polar → attracts water)
And Hydrophobic tails: two fatty acids (non-polar → repel water)
How do phospholipids arrange in water?
Hydrophilic heads face outward towards water.
Hydrophobic tails face inward.
What is the function of the hydrophobic centre of the bilayer?
The hydrophobic bilayer centre acts as a barrier to water-soluble substances.
Describe the steps of the emulsion test for lipids.
Place food sample in a test tube.
Add 2 cm³ of ethanol.
Shake well for 2 minutes
Add 2 cm³ distilled water.
What indicates a positive result for lipids in the emulsion test?
Positive result = milky white emulsion
